It’s a statement as much as a technique. “I can’t see what I’m doing, so I don’t have to worry about getting it inside the lines,” T.J. Walton says.

Walton has been painting outside of those lines in Provincetown, Massachusetts, since 1989. The oldest continuously running art colony in the United States makes for an appropriate backdrop to work that often has a rustic, vintage look.

She uses a variety of materials: canvas, wood, even painters’ dropcloths that are “raw and unintentional, with the natural markings of a working person. The beauty shines through because of the simplicity of what you do,” she says. That simple style is her trademark: it’s only upon looking more deeply at her pieces that a viewer starts seeing layer...